Semiconductor device having via connecting between interconnects

ABSTRACT

A first insulating film is provided between a lower interconnect and an upper interconnect. The lower interconnect and the upper interconnect are connected to each other by way of a via formed in the first insulating film. A dummy via or an insulating slit is formed on/in the upper interconnect near the via.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. application Ser. No.11/000,904, filed Dec. 2, 2004, now U.S. Pat. No. 7,439,623 claimingpriority of Japanese Patent Application No. 2003-404437 filed on Dec. 2,2003, the entire contents of each of which are incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to interconnection structures and methodsfor forming the structures.

To meet recent increase in the speed and integration density ofelectronic devices such as semiconductor devices, copper (Cu) having lowresistance has been more frequently used as an interconnect material.

FIG. 19B is a cross-sectional view showing an example of a conventionalmultilevel interconnection structure formed by using Cu. As shown inFIG. 19B, a first interconnect 2 is buried in an insulating film 1formed on a semiconductor substrate (not shown), and a SiN film 3, aSiO₂ film 4 and a FSG (fluorine-doped silicate glass, i.e.,fluorine-doped silicon oxide) film 5 are formed in this order over theinsulating film 1 and the first interconnect 2. A via hole 6 is formedthrough the SiO₂ film 4 and the SiN film 3 to reach the firstinterconnect 2. An interconnect trench 7 is formed in the FSG film 5 toreach the via hole 6. A barrier film 8 and a Cu film 9 are buried inthis order in the via hole 6 and the interconnect trench 7, therebyforming a via 10 and a second interconnect 11 in the via hole 6 and theinterconnect trench 7, respectively. A SiN film 12 is formed on the FSGfilm 5 and the second interconnect 11.

As shown in FIG. 19B, the first interconnect 2 and the secondinterconnect 11 are electrically connected to each other by way of thevia 10. Each of the first interconnect 2 and the second interconnect 11is electrically connected to another element (now shown) or an externalelectrode (not shown.) In this manner, the first interconnect 2, the via10 and the second interconnect 11 constitute part of a closed circuit inactual use.

FIG. 19C is a plan view showing the multilevel interconnection structureshown in FIG. 19B when viewed above. As shown in FIG. 19C, the firstinterconnect 2 has a width smaller than that of the second interconnect11. Specifically, the width of the first interconnect 2 is 0.2 μm, thediameter of the via 10 (the via hole 6) is 0.20 μM, and the width of thesecond interconnect 11 is 10 μm.

FIGS. 18A through 18C and 19A are cross-sectional views showingrespective process steps of a conventional method for forming themultilevel interconnection structure shown in FIG. 19B (see JapaneseUnexamined Patent Publication (Kokai) No. 2000-331991.)

First, as shown in FIG. 18A, an insulating film 1 is formed on thesurface of a semiconductor substrate (not shown), and then a firstinterconnect 2 is formed in the insulating film 1.

Next, as shown in FIG. 18B, a SiN film 3, a SiO₂ film 4 and a FSG film 5are formed in this order over the insulating film 1 and the firstinterconnect 2 by a plasma chemical vapor deposition (plasma CVD)process. Thereafter, lithography and dry etching are alternatelyperformed twice (i.e., lithography and dry etching are each performedtwice), thereby forming a via hole 6 through the SiO₂ film 4 and the SiNfilm 3 to reach the first interconnect 2 and also forming aninterconnect trench 7 in the FSG film 5 to reach the via hole 6.

Then, as shown in FIG. 18C, a barrier film 8 is deposited by a physicalvapor deposition (PVD) process to fill the via hole 6 and theinterconnect trench 7. Then, a Cu film 9 is formed by a plating processon the barrier film 8 to completely fill the via hole 6 and theinterconnect trench 7.

Thereafter, as shown in FIG. 19A, parts of the barrier film 8 and the Cufilm 9 extending off the interconnect trench 7 are removed by achemical/mechanical polishing (CMP) process. In this manner, a secondinterconnect 11 is formed in the interconnect trench 7, and a via 10connecting the first interconnect 2 and the second interconnect 11 toeach other is formed in the via hole 6.

Lastly, a SiN film 12 is deposited over the FSG film 5 and the secondinterconnect 11 (the Cu film 9), thus completing the multilevelinterconnection structure shown in FIG. 19B.

SUMMARY OF THE INVENTION

However, this conventional multilevel interconnection structure has thefollowing drawbacks. A large number of vacancies are present in the Cufilm 9 deposited by plating. When the multilevel interconnectionstructure is held at high temperature, these vacancies move along thegradient of stress. Specifically, if compressive stress inside the via10 is higher than compressive stress inside the second interconnect 11,i.e., if tensile stress inside the via 10 is lower than tensile stressinside the second interconnect 11, vacancies flow from the secondinterconnect 11 into the via 10. In particular, in a multilevelinterconnection structure as shown in FIGS. 19B and 19C, the volume ofthe second interconnect 11 is much greater than that of the via 10, sothat a large number of vacancies flow from the second interconnect 11into the via 10. As a result, as shown in FIG. 20A, plastic deformationoccurs in a part of the Cu film 9 constituting the via 10, so that avoid 13 is created in the via hole 6. If the electrical connectionbetween the first interconnect 2 and the second interconnect 11 isbroken by this void 13, the device malfunctions.

It is therefore an object of the present invention to achieve ahighly-reliable multilevel interconnection structure which does notcause malfunction even when the structure is held at high temperature.

To achieve the object, a first interconnection structure according tothe present invention includes: a lower interconnect; an upperinterconnect; a first insulating film provided between the lowerinterconnect and the upper interconnect; and a second insulating filmprovided under the first insulating film, wherein the lower interconnectand the upper interconnect are connected to each other by way of a viaformed in the first insulating film, at least one dummy via is connectedto the upper interconnect, the lower interconnect is formed in thesecond insulating film, and the bottom of the dummy via is located inthe second insulating film.

In the first interconnection structure, the dummy via is provided on theupper interconnect near the via, so that vacancies in a part of aconductive film constituting the upper interconnect are divided andrespectively flow into the via and the dummy via. That is, the dummy viareduces the stress gradient from the upper interconnect to the via.Accordingly, even when the interconnection structure is held at hightemperature, flowing of vacancies from the upper interconnect to the viais suppressed. As a result, plastic deformation of a part of theconductive film constituting the via, i.e., occurrence of a void insidethe via hole, is suppressed, so that a highly-reliable multilevelinterconnection structure which does not cause malfunction even whenheld at high temperature is implemented.

In addition, in the first interconnection structure, the bottom of thedummy via is located in the second insulating film below the firstinsulating film. Therefore, a hole for forming the dummy via is deeperthan a hole for forming the via (i.e., a via hole.) Accordingly, thestress gradient between the upper interconnect and the dummy via issteeper than that between the upper interconnect and the via. As aresult, flowing of vacancies from the part of the conductive filmconstituting the upper interconnect into the dummy via precedes thatinto the via. This more effectively suppresses plastic deformation ofthe part of the conductive film constituting the via, i.e., occurrenceof a void in the via hole. As a result, the reliability of themultilevel interconnection structure is further enhanced.

A dummy via and a dummy interconnect herein means a pseudo via or apseudo interconnect which do not constitute a closed circuit in actualuse of a device with an interconnection structure including these viaand interconnect (i.e., no current flows therein during actual use ofthe device.)

In the first interconnection structure, the bottom of the dummy via maybe connected to a dummy interconnect formed in the second insulatingfilm. Then, a hole for forming a dummy via is easily formed by etchingthe first insulating film with the dummy interconnect used as an etchingstopper.

In the first interconnection structure, a third insulating film may beformed on the upper interconnect, and the dummy via may be formed in thethird insulating film such that the bottom of the dummy via is connectedto the upper interconnect.

In the first interconnection structure, the dummy via preferably has adiameter smaller than that of the via.

Then, the diameter of the hole for the dummy via is smaller than that ofthe hole for the via (i.e., the via hole). In other words, the volume ofthe dummy via is smaller than that of the via. Accordingly, the stressgradient between the upper interconnect and the dummy via is steeperthan that between the upper interconnect and the via. As a result,flowing of vacancies from a part of the conductive film constituting theupper interconnect into the dummy via precedes that into the via. Thismore effectively suppresses plastic deformation of a part of theconductive film constituting the via, i.e., occurrence of a void in thevia hole. As a result, the reliability of the multilevel interconnectionstructure is further enhanced.

In the first interconnection structure, the dummy via is preferablysubstantially rectangular in a plan view, and the length of the dummyvia and the width of the upper interconnect are provided along the samedirection in the plan view.

Then, vacancies which are present in a part of the conductive filmconstituting the upper interconnect opposite the via with respect to thedummy via flow into the dummy via, so that it is possible to preventthese vacancies from reaching the via. This more effectively suppressesplastic deformation of a part of the conductive film constituting thevia, i.e., occurrence of a void in the via hole. As a result, thereliability of the multilevel interconnection structure is furtherenhanced.

In the first interconnection structure, the via may be substantiallycircular in a plan view, and the dummy via may have a shape differentfrom that of the via in the plan view.

In the first interconnection structure, the dummy via is preferablycloser to a center of the upper interconnect than the via is. In otherwords, the distance between the via and the end of the upperinterconnect opposite the via with respect to the dummy via (which willbe also referred to as the end of the upper interconnect toward thedummy via) is preferably longer than the distance between the via andthe other end of the upper interconnect, i.e., the end of the upperinterconnect toward the via.

Then, the distance between the via and the end of the upper interconnecttoward the dummy via is longer than the distance between the via and theother end of the upper interconnect. In other words, a first region inthe upper interconnect between the end thereof toward the dummy via andthe via is larger than a second region in the upper interconnect betweenthe other end thereof and the via. Therefore, the first region containsa larger number of vacancies than the second region. In addition, thedummy via is provided in this first region, so that vacancies moreeffectively flow into the dummy via. This more effectively suppressesplastic deformation of a part of the conductive film constituting thevia, i.e., occurrence of a void in the via hole. As a result, thereliability of the multilevel interconnection structure is furtherenhanced.

In the first interconnection structure, the via and the dummy via arepreferably spaced at a distance of 1 μm or less.

Then, the effect of making part of vacancies which are to flow into thevia flow into the dummy via is ensured. The space between a via (a viahole) and a dummy via (a dummy hole) herein means the space between theedge of the via toward the dummy via and the edge of the dummy viatoward the via. The minimum space is set in accordance with the minimumisolation width between interconnects or vias defined by the designrule, for example.

A second interconnection structure according to the present inventionincludes: a lower interconnect; an upper interconnect; and a firstinsulating film provided between the lower interconnect and the upperinterconnect, wherein the lower interconnect and the upper interconnectare connected to each other by way of a via formed in the firstinsulating film, and at least one insulating slit is formed in the upperinterconnect.

In the second interconnection structure, the insulating slit is providedin the upper interconnect near the via, so that the tensile stress on apart of the upper interconnect near the via is lower than that on theother part of the upper interconnect. That is, the insulating slitreduces the stress gradient from the upper interconnect to the via.Accordingly, even when the interconnection structure is held at hightemperature, flowing of vacancies from the upper interconnect toward thevia is suppressed. In addition, the insulating slit is made of amaterial different from that for a conductive film constituting theupper interconnect and the via, so that the insulating slit acts as abarrier against movement of atoms or vacancies in the conductive film.This prevents convection of atoms inside the upper interconnect and thevia or accumulation of vacancies on the bottom of the via. As a result,plastic deformation of a part of the conductive film constituting thevia, i.e., occurrence of a void inside the via hole, is suppressed, sothat a highly-reliable multilevel interconnection structure which doesnot cause malfunction even when held at high temperature is implemented.

In the second interconnection structure, the insulating slit may be apart of the first insulating film provided between the lowerinterconnect and the upper interconnect, for example.

In the second interconnection structure, the insulating slit may be incontact with a portion of the upper interconnect connected to the via.In such a case, if the insulating slit is substantially rectangular in aplan view, the length of the insulating slit is greater than or equal totwice and less than or equal to four times as large as the diameter ofthe via in the plan view, and a longer side of the insulating slit inthe plan view is in contact with the portion of the upper interconnectconnected to the via, the foregoing advantages are obtained.

In the second interconnection structure, it is preferable that theinsulating slit is substantially rectangular in a plan view, the lengthof the insulating slit is greater than or equal to twice and less thanor equal to ten times as large as the diameter of the via in the planview, and the length of the insulating slit and the width of the upperinterconnect are provided along the same direction in the plan view.

Then, even in a case where the insulating slit is apart from a portionof the upper interconnect connected to the via, the following advantageis obtained. Flowing of vacancies which are present in a part of aconductive film constituting the upper interconnect opposite the viawith respect to the insulating slit is blocked by the insulating slit,so that these vacancies do not reach the via. In addition, theinsulating slit is closer to the center of the upper interconnect thanthe via is. In other words, the distance between the via and the end ofthe upper interconnect opposite the via with respect to the insulatingslit (which will be also referred to as the end of the upperinterconnect toward the insulating slit) is longer than the distancebetween the via and the other end of the upper interconnect, i.e., theend of the upper interconnect toward the via, so that a first region inthe upper interconnect between the end thereof toward the insulatingslit and the via is larger than a second region in the upperinterconnect between the other end thereof and the via. Therefore, thefirst region contains a larger number of vacancies than the secondregion. In addition, the insulating slit is provided in this firstregion, so that movement of vacancies is more effectively prevented bythe insulating slit. This more effectively suppresses plasticdeformation of a part of the conductive film constituting the via, i.e.,occurrence of a void in the via hole. As a result, the reliability ofthe multilevel interconnection structure is further enhanced.

In the second interconnection structure, the insulating slit ispreferably closer to a center of the upper interconnect than the via is.

In the second interconnection structure, the via and the insulating slitare preferably spaced at a distance of 1 μm or less.

Then, the effect of preventing movement of vacancies which are to flowinto the via by using the insulating slit is obtained. The space betweena via (a via hole) and an insulating slit herein means the space betweenthe edge of the via toward the insulating slit and the edge of theinsulating slit toward the via. As described above, the insulating slitmay be in contact with the portion of the upper interconnect connectedto the via. In this case, the space between the via and the insulatingslit is zero.

A third interconnection structure according to the present inventionincludes: a lower interconnect; an upper interconnect; and a firstinsulating film provided between the lower interconnect and the upperinterconnect, wherein the lower interconnect and the upper interconnectare connected to each other by way of a via formed in the firstinsulating film, the upper interconnect is divided into a firstinterconnect portion having a relatively large interconnect width and asecond interconnect portion having a relatively small interconnectwidth, the via is connected to the second interconnect portion, at leastone dummy portion connected to the upper interconnect is provided on thefirst insulating film, and a distance between the dummy portion and abranch point between the first interconnect portion and the secondinterconnect portion is smaller than a distance between the dummyportion and an edge of the second interconnect portion opposite to thebranch point.

In the third interconnection structure, not only advantages similar tothose obtained by the first interconnection structure but also thefollowing advantage is obtained. Vacancies which are to enter a secondinterconnect portion (a narrow interconnect portion) from a firstinterconnect portion (a wide interconnect portion) and flow into the viaare effectively captured in the dummy portion. As a result, the numberof devices malfunctioning when being held at high temperature is furtherreduced.

In the third interconnection structure, the dummy portion may beconnected to the first interconnect portion or the second interconnectportion, and a distance between the dummy portion and the branch pointmay be smaller than a distance between the dummy portion and an edge ofthe second interconnect portion opposite to the branch point. Thedistance between the dummy portion and the branch point may be 1 μm orless. The dummy portion may have a shape similar to that of the via orbe substantially rectangular in a plan view.

In the third interconnection structure, if the second interconnectportion has an interconnect width of 0.20 μm or less, the foregoingadvantages are more remarkable than those in a conventionalinterconnection structure.

A first method for forming an interconnection structure according to thepresent invention includes the steps of: depositing a first insulatingfilm on a lower interconnect; forming, in the first insulating film, avia hole reaching the lower interconnect, at least one dummy holelocated near the via hole, and an upper interconnect trench connected tothe via hole and the dummy hole; and depositing a conductive material inthe upper interconnect trench, the via hole and the dummy hole, therebyforming an upper interconnect, a via for connecting the lowerinterconnect and the upper interconnect to each other, and a dummy viaconnected to the upper interconnect and insulated from the lowerinterconnect, wherein the lower interconnect is formed in a secondinsulating film under the first insulating film, and the dummy hole isformed such that the bottom of the dummy hole is located in the secondinsulating film.

With the first method, the first interconnection structure according tothe present invention is formed, so that advantages similar to thoseobtained by the first interconnection structure are obtained. To form avia or an upper interconnect, a damascene process such as a dualdamascene process or other processes may be used.

A second method for forming an interconnection structure according tothe present invention includes the steps of: depositing a firstinsulating film on a lower interconnect; forming, in the firstinsulating film, a via hole reaching the lower interconnect and an upperinterconnect trench connected to the via hole; depositing a conductivematerial in the upper interconnect trench and the via hole, therebyforming an upper interconnect and a via for connecting the lowerinterconnect and the upper interconnect to each other; depositing asecond insulating film on the upper interconnect; forming, in the secondinsulating film, a dummy hole reaching the upper interconnect andlocated near the via; and depositing a conductive material in the dummyhole, thereby forming at least one dummy via.

With the second method, the first interconnection structure according tothe present invention is formed, so that advantages similar to thoseobtained by the first interconnection structure are obtained. To form avia or an upper interconnect, a damascene process such as a dualdamascene process or other processes may be used.

In the first or second method, the via hole and the dummy hole arepreferably spaced at a distance of 1 μm or less.

Then, part of vacancies which are to flow into the via flow into thedummy via.

A third method for forming an interconnection structure according to thepresent invention includes the steps of: depositing a first insulatingfilm on a lower interconnect; forming, in the first insulating film, avia hole reaching the lower interconnect and an upper interconnecttrench connected to the via hole; and depositing a conductive materialin the upper interconnect trench and the via hole, thereby forming anupper interconnect and a via for connecting the lower interconnect andthe upper interconnect to each other, wherein the step of forming thevia hole and the upper interconnect trench includes the step of leavingpart of the first insulating film in the upper interconnect trench nearthe via hole, thereby forming an insulating slit.

With the third method, the second interconnection structure according tothe present invention is formed, so that advantages similar to thoseobtained by the second interconnection structure are obtained. To form avia or an upper interconnect, a damascene process such as a dualdamascene process or other processes may be used.

A fourth method for forming an interconnection structure according tothe present invention includes the steps of: depositing a firstinsulating film on a lower interconnect; forming, in the firstinsulating film, a via hole reaching the lower interconnect, an upperinterconnect trench connected to the via hole and divided into a firsttrench with a relatively large width and a second trench with arelatively small width, and a recess provided near a branch pointbetween the first trench and the second trench; and depositing aconductive material in the upper interconnect trench, the via hole andthe recess, thereby forming an upper interconnect, a via for connectingthe lower interconnect and the upper interconnect to each other and adummy portion connected to the upper interconnect and insulated from thelower interconnect, wherein a first interconnect portion constitutingthe upper interconnect is formed in the first trench and a secondinterconnect portion constituting the upper interconnect is formed inthe second trench.

With the fourth method, the third interconnection structure according tothe present invention is formed, so that advantages similar to thoseobtained by the third interconnection structure are obtained. To form avia or an upper interconnect, a damascene process such as a dualdamascene process or other processes may be used.

As described above, according to the present invention, a dummy via oran insulating slit is provided on/in the upper interconnect near via, sothat it is possible to prevent flowing of vacancies from an upperinterconnect toward a via constituting a closed circuit together withthe upper interconnect in actual use. Accordingly, plastic deformationof a part of a conductive film constituting the via, i.e., occurrence ofa void in a via hole, is suppressed, resulting in a highly-reliablemultilevel interconnection structure. The present invention relates tointerconnection structures and methods for forming the structures, andis useful especially when applied to electronic devices such assemiconductor devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are cross-sectional views showing respective processsteps of a method for forming an interconnection structure according toa first embodiment of the present invention.

FIGS. 2A and 2B are cross-sectional views showing respective processsteps of the method for forming the interconnection structure of thefirst embodiment, and FIG. 2C is a plan view showing the interconnectionstructure of the first embodiment.

FIG. 3 is a graph showing how an effect achieved by the first embodiment(i.e., the effect of suppressing malfunction after a device has beenheld at high temperature) depends on a via-to-dummy via space.

FIG. 4 is a plan view showing an interconnection structure according toa modified example of the first embodiment.

FIG. 5 is a graph showing how an effect achieved by the modified exampleof the first embodiment (i.e., the effect of suppressing malfunctionafter a device has been held at high temperature) depends on aninterconnect width (i.e., the width of a narrow interconnect on which avia is formed.)

FIGS. 6A through 6C are cross-sectional views showing respective processsteps of a method for forming an interconnection structure according toa second embodiment of the present invention.

FIGS. 7A and 7B are cross-sectional views showing respective processsteps of the method for forming the interconnection structure of thesecond embodiment, and FIG. 7C is a plan view showing theinterconnection structure of the second embodiment.

FIG. 8A is a cross-sectional view showing an interconnection structureaccording to a third embodiment of the present invention, and FIG. 5B isa plan view showing the interconnection structure of the thirdembodiment.

FIG. 9A is a cross-sectional view showing an interconnection structureaccording to a fourth embodiment of the present invention, and FIG. 9Bis a plan view showing the interconnection structure of the fourthembodiment.

FIG. 10 is a plan view showing an interconnection structure according toa modified example of the fourth embodiment.

FIGS. 11A through 11C are cross-sectional views showing respectiveprocess steps of a method for forming an interconnection structureaccording to a fifth embodiment of the present invention.

FIGS. 12A through 12C are cross-sectional views showing respectiveprocess steps of the method for forming the interconnection structure ofthe fifth embodiment.

FIGS. 13A and 13B are cross-sectional views showing respective processsteps of the method for forming the interconnection structure of thefifth embodiment, and FIG. 13C is a plan view showing theinterconnection structure of the fifth embodiment.

FIGS. 14A through 14C are cross-sectional views showing respectiveprocess steps of a method for forming an interconnection structureaccording to a sixth embodiment of the present invention.

FIGS. 15A and 15B are cross-sectional views showing respective processsteps of the method for forming the interconnection structure of thesixth embodiment, and FIG. 15C is a plan view showing theinterconnection structure of the sixth embodiment.

FIG. 16 is a graph showing an effect achieved by the sixth embodiment(i.e., the effect of suppressing malfunction after a device has beenheld at high temperature).

FIG. 17A is a cross-sectional view showing an interconnection structureaccording to a seventh embodiment of the present invention, and FIG. 17Bis a plan view showing the interconnection structure of the seventhembodiment.

FIGS. 18A through 18C are cross-sectional views showing respectiveprocess steps of a conventional method for forming an interconnectionstructure.

FIGS. 19A and 19B are cross-sectional views showing respective processsteps of the conventional method for forming an interconnectionstructure, and FIG. 19C is a plan view showing the conventionalinterconnection structure.

FIG. 20A is a view for explaining problems in the conventionalinterconnection structure, and FIG. 20B is an illustration forexplaining a result of an examination carried out by the presentinventor on problems in the conventional interconnection structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Principle of the PresentInvention

First, for a phenomenon in which a void occurs in a via hole in aconventional multilevel interconnection structure, a result of anexamination carried out by the present inventor (i.e., a mechanism ofthis phenomenon) will be described.

A metal film is affected by its surrounding films depending on aninterconnection structure including the metal film. For example, asshown in FIG. 20B, a metal film (e.g., a Cu film) formed in part of aninterconnect trench with a narrow interconnect width provided in aninsulating film is slightly stretched by its surrounding insulatingfilms. That is, this Cu film is under relatively low tensile stress. Onthe other hand, a Cu film formed in part of the interconnect trench witha wide interconnect width in the insulating film is strongly stretchedby its surrounding insulating films. That is, this Cu film is underrelatively high tensile stress. Such tensile stress occurs mainlybecause of the difference in a thermal expansion coefficient between ametal film and an insulating film or because of shrinkage of the metalfilm resulting from thermal load in a subsequent step. The tensilestress greatly changes depending on the shapes of the interconnecttrench and the via hole, the placement density and others.

A metal film made of Cu or another metal generally has a crystalstructure in which atoms are relatively regularly arranged immediatelyafter formation of the film. To form a Cu film, which is mainly used asan interconnect material, is generally formed by electroplating. The Cufilm formed by electroplating contains a large number of vacancies. Inaddition, in the interconnection structure shown in FIG. 20B, vacanciescontained in the Cu film are more likely to gather in a portion of theCu film where tensile stress is low than in a portion thereof wheretensile stress is high. This is because stress applied from theneighboring insulating films to the crystal structure of the Cu film isrelaxed by entering of vacancies into the portion of the Cu film withlow tensile stress, i.e., entering of Cu atoms into the portion of theCu film with high tensile stress.

Accordingly, when the flexibility of Cu atoms and vacancies is enhancedby, for example, application of heat to the interconnection structure,vacancies move along the stress gradient in the Cu film, i.e., move fromthe portion of the Cu film with high tensile stress to the portion ofthe Cu film with low tensile stress (where the direction of movement ofCu atoms is opposite to that of vacancies.) As a result, vacanciesreadily gather in part of the interconnection structure with a narrowinterconnect width or the bottom or corners of the interconnect, andthus voids readily occur.

Based on the foregoing finding, the following embodiments of the presentinvention are made to implement a technical idea in which the stressgradient in a conductive film serving as an interconnect is reduced soas to suppress the movement of vacancies in the conductive film andthereby to avoid occurrence of a void in the interconnect afterformation thereof

Embodiment 1 A Case where a Via and a Dummy Via are Provided in the SameLayer (Basic Structure)

Hereinafter, an interconnection structure and a method for forming thestructure according to a first embodiment of the present invention willbe described with reference to the drawings.

FIG. 2B is a cross-sectional view showing the interconnection structureof the first embodiment. As shown in FIG. 2B, a first interconnect 102Aand a dummy interconnect 102B are buried in an insulating film 101formed on the semiconductor substrate (not shown). A SiN film 103, aSiO₂ film 104 and an FSG film 105 are stacked over the insulating film101, the first interconnect 102A and the dummy interconnect 102B. A viahole 106A and a dummy via hole (dummy hole) 106B are formed in the SiO₂film 104 and the SiN film 103 to reach the first interconnect 102A andthe dummy interconnect 102B, respectively. An interconnect trench 107 isformed in the FSG film 105 to be connected to the via hole 106A and thedummy hole 106B. A barrier film 108 and a Cu film 109 are buried in thisorder in the via hole 106A, the dummy hole 106B and the interconnecttrench 107, thereby forming a via 110A, a dummy via 110B, and a secondinterconnect 111 in the via hole 106A, the dummy hole 106B and theinterconnect trench 107, respectively. The dummy via 110B is connectedto the second interconnect 111 near the via 110A. A SiN film 112 isformed on the FSG film 105 and the second interconnect 111.

As shown in FIG. 2B, the first interconnect 102A and the secondinterconnect 111 are electrically connected to each other by way of thevia 110A. Each of the first interconnect 102A and the secondinterconnect 111 is electrically connected to another element (nowshown) or an external electrode (not shown.) In this manner, the firstinterconnect 102A, the via 110A and the second interconnect 111constitute part of a closed circuit in actual use. On the other hand,neither the dummy interconnect 102B nor the dummy via 110B constitutes aclosed circuit in actual use. That is, even if the dummy interconnect102B and the dummy via 110B are omitted in the interconnection structureshown in FIG. 2B, a device with this interconnection structure isoperable at least immediately after fabrication.

FIG. 2C is a plan view showing the multilevel interconnection structureshown in FIG. 2B when viewed above. As shown in FIG. 2C, in thisembodiment, each of the first interconnect 102A and the dummyinterconnect 102B has a width smaller than that of the secondinterconnect 111. Specifically, the width of each of the firstinterconnect 102A and the dummy interconnect 102B is, for example, 0.2μm, the diameter of each of the via 110A (the via hole 106A) and thedummy via 110B (the dummy hole 106B) is, for example, 0.20 μm, and thewidth of the second interconnect 111 is, for example, 10 μm. The spacebetween the via 110A and the dummy via 110B, more specifically, thespace between the edge of the via 110A toward the dummy via 110B and theedge of the dummy via 110B toward the via 110A is 0.2 μm, for example.In the present invention, if the planar shape (the shape in plan view)of a via (via hole) is a circle, the diameter of the via (via hole) isthe diameter of this circle whereas if the planar shape of the via (viahole) is a square, the diameter of the via (via hole) is the length of aside of this square.

FIGS. 1A through 1C and FIG. 2A are cross-sectional views showingrespective process steps of a method for forming the multilevelinterconnection structure shown in FIG. 2B according to the firstembodiment.

First, as shown in FIG. 1A, an insulating film 101 is formed on thesurface of a semiconductor substrate (not shown), and then a firstinterconnect 102A and a dummy interconnect 102B are formed in theinsulating film 101.

Next, as shown in FIG. 1B, a SiN film 103, a SiO₂ film 104 and a FSGfilm 105 are formed in this order over the insulating film 101, thefirst interconnect 102A and the dummy interconnect 102B by a plasma CVDprocess, for example. Thereafter, lithography and dry etching arealternately performed twice (i.e., lithography and dry etching are eachperformed twice), thereby forming a via hole 106A and a dummy hole 106Bin the SiO₂ film 104 and the SiN film 103 to reach the firstinterconnect 102A and the dummy interconnect 102B, respectively, andalso forming an interconnect trench 107 in the FSG film 105 to reach thevia hole 106A and the dummy hole 106B.

Then, as shown in FIG. 1C, a barrier film 108 is deposited by a PVDprocess, for example, to partly fill the via hole 106A, the dummy hole106B and the interconnect trench 107. Then, a Cu film 109 is formed by aplating process, for example, on the barrier film 108 to completely fillthe via hole 106A, the dummy hole 106B and the interconnect trench 107.

Thereafter, as shown in FIG. 2A, parts of the barrier film 108 and theCu film 109 extending off the interconnect trench 107 are removed by aCMP process, for example. In this manner, a second interconnect 111 isformed in the interconnect trench 107. In addition, a via 110A is formedin the via hole 106A to connect the first interconnect 102A and thesecond interconnect 111 to each other, and a dummy via 110B is formed inthe dummy hole 106B to connect the dummy interconnect 102B and thesecond interconnect 111 to each other. The dummy via 110B is notconnected to the first interconnect 102A.

Lastly, a SiN film 112 is deposited over the FSG film 105 and the secondinterconnect 111 (the Cu film 109), thus completing the multilevelinterconnection structure shown in FIG. 2B.

With the foregoing interconnection structure and the method for formingthe structure according to the first embodiment, a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The dummy via 110B is provided on the secondinterconnect 111 near the via 110A, so that vacancies in a part of theconductive film (the Cu film 109) constituting the second interconnect111 are divided and respectively flow into the via 110A and the dummyvia 10B. That is, the dummy via 110B reduces the number of vacanciesflowing into each via so that the stress gradient from the secondinterconnect 111 to the via 110A is reduced. Accordingly, even when theinterconnection structure is held at high temperature, flowing ofvacancies from the second interconnect 111 into the via 110A issuppressed. As a result, plastic deformation of a part of the conductivefilm (the Cu film 109) constituting the via 110A, i.e., occurrence of avoid inside the via hole 106A, is suppressed, so that a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented.

In the first embodiment, the dummy interconnect 102B is provided underthe dummy via 110B (the dummy hole 106B). Accordingly, the dummy hole106B is easily formed by etching the SiO₂ film 104 and the SiN film 103with the dummy interconnect 102B used as an etching stopper.

In the first embodiment, the space between the via 110A and the dummyvia 110B (i.e., the space between the via hole 106A and the dummy hole106B: hereinafter referred to as a via-to-dummy via space) is preferablyas small as possible. To obtain the effect of reducing the number ofvacancies flowing into the via 110A by using the dummy via 110B, thevia-to-dummy via space is preferably 25 μm or less and is morepreferably 1 μm or less. The minimum via-to-dummy via space can be setin accordance with the minimum isolation width (e.g., 0.2 μm) betweeninterconnects or vias defined by the design rule, for example. If theminimum isolation width between interconnects is set substantially equalto the minimum interconnect width, the minimum via-to-dummy via spacemay be set in accordance with the minimum interconnect width.

FIG. 3 shows how an effect achieved by the present invention (i.e., theeffect of suppressing malfunction after a device has been held at hightemperature) depends on a via-to-dummy via space. In FIG. 3, theordinate indicates “the number of devices malfunctioning after beingheld at high temperature” and the abscissa indicates “via-to-dummy viaspace (μm)”. The “without dummy via” in the abscissa corresponds to acase where the via-to-dummy via space is unlimited. As shown in FIG. 3,as the via-to-dummy via space decreases, the number of malfunctioningdevices decreases. In other words, the effect of the present inventionbecomes remarkable. This is because as the via-to-dummy via spacedecreases, vacancies which are to gather in the via are more likely tobe absorbed in the dummy via.

However, as shown in FIG. 3, when the via-to-dummy via space is 30 μm ormore, it is difficult to effectively suppress occurrence of a void inthe via by using the dummy via. This is because of the following reason.Vacancies moves within a limited range and therefore it is difficult forthe dummy via to absorb vacancies which are to enter the via when thevia-to-dummy via space is large. Accordingly, when the via-to-dummy viaspace is large, especially when the via-to-dummy via space greatlyexceeds 30 μm the incidence of voids is substantially equal to that inthe case of “without dummy via”. As a result, the number of devicesmalfunctioning after being held at high temperature is not sufficientlyreduced.

In the first embodiment, the number of dummy vias 110B provided for onevia 110A is preferably as large as possible. Specifically, it ispreferable to provide dummy vias 110B as many as possible on a part ofthe second interconnect 111 where the dummy vias 110B do not affectcircuit operation.

Modified Example of Embodiment 1

Hereinafter, an interconnection structure and a method for forming thestructure according to a modified example of the first embodiment willbe described with reference to the drawings.

FIG. 4 is a plan view showing the interconnection structure of themodified example of the first embodiment.

As shown in FIG. 4, this modified example is different from the firstembodiment (see FIG. 2C) in the following ways. First, the secondinterconnect 111 includes: a wide interconnect portion 111 a having awidth of 10 μm, for example; and a narrow interconnect portion 111 bhaving a width of 0.20 μm, for example, and branching off from the wideinterconnect portion 111 a. Second, the via 110A (the via hole 106A) isconnected to the narrow interconnect portion 111 b. Third, a pluralityof dummy vias 110B (the dummy holes 106B) are connected to the branchpoint between the wide interconnect portion 111 a and the narrowinterconnect portion 111 b and to portions of the wide interconnectportion 111 a near the branch point.

That is, the method for forming the interconnection structure accordingto this modified example is different from that of the first embodimentin that in the process step shown in FIG. 1B, the interconnect trench107 divided into a first trench with a relatively large width is formedand a second trench with a relatively small width and the dummy holes106B are also formed near the branch point between the first trench andthe second trench.

In this modified example, not only the advantages obtained by the firstembodiment but also the following advantage is obtained. Vacancies whichare to enter the narrow interconnect portion 111 b from the wideinterconnect portion 111 a and flow into the via 110A are effectivelycaptured in the dummy vias 110B. As a result, the number of devicesmalfunctioning when being held at high temperature is further reduced.

In this modified example, one or more dummy vias 110B (dummy holes 106B)may be connected to the branch point between the wide interconnectportion 111 a and the narrow interconnect portion 111 b or portions ofthe wide interconnect portion 111 a near the branch point. However, thedummy vias 110B are not necessarily provided only at the branch point orits neighboring portions. For example, if a dummy via 110B is located inpart of the narrow interconnect portion 111 b relatively near the wideinterconnect portion 111 a, most of vacancies which are to enter the via110A are captured in the dummy via 110B before reaching the via 110A.Accordingly, it is possible to prevent occurrence of a void in the via110A.

In this modified example, the distance between the branch point and eachof the dummy vias 110B is preferably smaller than the distance betweenan edge of the wide interconnect portion 111 a opposite to the branchpoint and each of the dummy vias 110B.

In this modified example, dummy vias 110B each having substantially thesame shape as that of the via 110A in plan view are provided.Alternatively, dummy portions each having a shape (e.g., a rectangle)different from that of the via 110A in plan view may be provided.

FIG. 5 shows how an effect achieved by the dummy via 110B of thismodified example (i.e., a dummy portion formed in part of the wideinterconnect portion 111 a near the branch point, for example) dependson a via-formed interconnect width (i.e., the width of the narrowinterconnect portion 111 b where the via 110A is formed.) In FIG. 5, theordinate indicates “the number of devices malfunctioning after beingheld at high temperature” and the abscissa indicates “via-formedinterconnect width (μm)”. The “without dummy via” in the abscissacorresponds to a case where no dummy via 110B is provided on the wideinterconnect portion 111 a near the branch point. As shown in FIG. 5, ina case where the width of the interconnect portion 111 b on which thevia 110A is formed is about 10 μm, i.e., the width of the interconnectportion 111 b is substantially equal to that of the interconnect portion111 a to which the interconnect portion 111 b is connected, even if adummy via (dummy portion) is formed near the branch point between theseinterconnect portions, the number of malfunctioning devices does notchange greatly. That is, if the width of the interconnect portion 111 bon which the via 110A is formed is relatively large, the interconnectportion 111 b contains a large amount of metal. Accordingly, thisinterconnect portion 111 b is likely to contain a large number ofdefects such as voids caused by the presence of metal. As a result, thenumber of malfunctioning devices is relatively large depending on theamount of metal contained in the interconnect portion 111 b.

On the other hand, as the width of the interconnect portion 111 b onwhich the via 110A is formed decreases, the amount of metal contained inthe interconnect portion 111 b decreases. Accordingly, the number ofdefects occurring in the interconnect portion 111 b due to the presenceof metal slightly decreases. However, as the interconnect portion 111 bbecomes narrower, the diameter of the via 110A provided on theinterconnect portion 111 b decreases, so that defects such as voids aremore likely to concentrate in the via 110A. In view of this, as shown inFIG. 4, the dummy via (dummy portion) 110B is formed near the branchpoint between the narrow interconnect portion 111 b on which the via110A is formed and the wide interconnect portion 111 a. In this manner,the incidence of malfunction is reduced in accordance with reduction ofthe interconnect width of the narrow interconnect portion 111 b, asshown in FIG. 5. This is because the number of defects occurring in themetal film decreases with reduction of the interconnect width and, inaddition, defects which are to concentrate in the via are absorbed inthe dummy vias in advance. Specifically, as the width of theinterconnect portion 111 b on which the via 110A is formed decreases,i.e., the diameter of the via 110A decreases, a larger number of defectsare absorbed in the dummy vias 110B. This absorbing effect is remarkableespecially when the width of the narrow interconnect portion 111 b isabout 0.20 μm or less, as shown in FIG. 5.

Embodiment 2 A Case where a Via and a Dummy Via are Provided in the SameLayer (Without a Dummy Interconnect)

Hereinafter, an interconnection structure and a method for forming thestructure according to a second embodiment of the present invention willbe described with reference to the drawings.

FIG. 7B is a cross-sectional view showing the interconnection structureof the second embodiment. FIG. 7C is a plan view showing the multilevelinterconnection structure shown in FIG. 7B when viewed from above. InFIGS. 7B and 7C, components already described in the first embodimentwith reference to FIGS. 1A through 1C and 2A through 2C are denoted bythe same reference numerals, and detailed description thereof will beomitted.

As shown in FIGS. 7B and 7C, the second embodiment is different from thefirst embodiment in the following ways. The dummy interconnect 102B isnot provided, a dummy hole 106C deeper than the dummy hole 106B isprovided instead of the dummy hole 106B, and a dummy via 110C is formedin the dummy hole 106C instead of the dummy via 110B. That is, thebottom of the dummy via 110C (the dummy hole 106C) is located in aninsulating film 101, and the dummy hole 106C is deeper than a via hole106A.

In this embodiment, the dummy via 110C is also connected to a secondinterconnect 111 near the via 110A.

As shown in FIG. 7B, the dummy via 110C does not constitute a closedcircuit in actual use. In other words, even if the dummy hole 106C isomitted in the interconnection structure shown in FIG. 7B, a device withthis interconnection structure is operable at least immediately afterfabrication.

In addition, in this embodiment, a first interconnect 102A has a widthsmaller than that of the second interconnect 111, as shown in FIG. 7C.Specifically, the width of the first interconnect 102A is, for example,0.2 μm, the diameter of each of the via 110A (the via hole 106A) and thedummy via 110C (the dummy hole 106C) is, for example, 0.20 μm, and thewidth of the second interconnect 111 is, for example, 10 μm. The spacebetween the via 110A and the dummy via 110C, more specifically, thespace between the edge of the via 110A toward the dummy via 110C and theedge of the dummy via 110C toward the via 110A is 0.2 μm, for example.

FIGS. 6A through 6C and 7A are cross-sectional views showing respectiveprocess steps of a method for forming the multilevel interconnectionstructure shown in FIG. 7B according to the second embodiment.

First, as shown in FIG. 6A, an insulating film 101 is formed on thesurface of a semiconductor substrate (not shown), and then a firstinterconnect 102A is formed in the insulating film 101.

Next, as shown in FIG. 6B, a SiN film 103, a SiO₂ film 104 and a FSGfilm 105 are formed in this order over the insulating film 101 and thefirst interconnect 102A by a plasma CVD process, for example.Thereafter, lithography and dry etching are alternately performed twice(i.e., lithography and dry etching are each performed twice), therebyforming a via hole 106A in the SiO₂ film 104 and the SiN film 103 toreach the first interconnect 102A and also forming a dummy hole 106C inthe SiO₂ film 104, the SiN film 103 and the insulating film 101. Inaddition, an interconnect trench 107 is formed in the FSG film 105 toreach the via hole 106A and the dummy hole 106C.

Then, as shown in FIG. 6C, a barrier film 108 is deposited by a PVDprocess, for example, to partly fill the via hole 106A, the dummy hole106C and the interconnect trench 107. Then, a Cu film 109 is formed by aplating process, for example, on the barrier film 108 to completely fillthe via hole 106A, the dummy hole 106C and the interconnect trench 107.

Thereafter, as shown in FIG. 7A, parts of the barrier film 108 and theCu film 109 extending off the interconnect trench 107 are removed by aCMP process, for example. In this manner, a second interconnect 111 isformed in the interconnect trench 107. In addition, a via 110A is formedin the via hole 106A to connect the first interconnect 102A and thesecond interconnect 111 to each other. A dummy via 110C connected onlyto the second interconnect 111 is formed in the dummy hole 106C. Inother words, the dummy via 110C is not connected to the firstinterconnect 102A.

Lastly, a SiN film 112 is deposited over the FSG film 105 and the secondinterconnect 111 (the Cu film 109), thus completing the multilevelinterconnection structure shown in FIG. 7B.

With the foregoing interconnection structure and the method for formingthe structure according to the second embodiment, a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The dummy via 110C is provided on the secondinterconnect 111 near the via 110A, so that vacancies in a part of theconductive film (the Cu film 109) constituting the second interconnect111 are divided and respectively flow into the via 110A and the dummyvia 110C. That is, the dummy via 110C reduces the number of vacanciesflowing into each via so that the stress gradient from the secondinterconnect 111 to the via 110A is reduced. Accordingly, even when theinterconnection structure is held at high temperature, flowing ofvacancies from the second interconnect 111 into the via 110A issuppressed. As a result, plastic deformation of a part of the conductivefilm (the Cu film 109) constituting the via 110A, i.e., occurrence of avoid inside the via hole 106A, is suppressed, so that a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented.

In the second embodiment, the resultant multilevel interconnectionstructure is more reliable than that obtained in the first embodiment.This is because of the following reasons. In this embodiment, the dummyhole 106C is deeper than the via hole 106A. Accordingly, the stressgradient between the second interconnect 111 and the dummy via 110C issteeper than that between the second interconnect 111 and the via 110A,so that flowing of vacancies from the part of the conductive film (theCu film 109) constituting the second interconnect 111 into the dummy via110C precedes that into the via 110A. This more effectively suppressesplastic deformation of the part of the conductive film (the Cu film 109)constituting the via 110A, i.e., occurrence of a void in the via hole106A. As a result, the resultant multilevel interconnection structure ismore reliable than that obtained in the first embodiment.

In the second embodiment, the space between the via 110A and the dummyvia 110C (i.e., the space between the via hole 106A and the dummy hole106C: hereinafter referred to as a via-to-dummy via space) is preferablyas small as possible. To obtain the effect of reducing the number ofvacancies flowing into the via 110A by using the dummy via 110C, thevia-to-dummy via space is preferably 25 μm or less and is morepreferably 1 μm or less. Then, the effect of making part of vacancieswhich are to flow into the via 110A flow into the dummy via 110C isensured. The minimum via-to-dummy via space can be set in accordancewith the minimum isolation width (e.g., 0.2 μm) between interconnects orvias defined by the design rule, for example. If the minimum isolationwidth between interconnects is set substantially equal to the minimuminterconnect width, the minimum via-to-dummy via space may be set inaccordance with the minimum interconnect width.

In the second embodiment, the number of dummy vias 110C provided for onevia 110A is preferably as large as possible. Specifically, it ispreferable to provide dummy vias 110C as many as possible on a part ofthe second interconnect 111 where the dummy vias 110C do not affectcircuit operation.

In addition, in the second embodiment, if the second interconnect 111includes a wide interconnect portion having a width of, for example,about 10 μm and a narrow interconnect portion having a width of, forexample, about 0.20 μm or less and branching off from the wideinterconnect portion and if the via 110A (the via hole 106A) isconnected to the narrow interconnect portion, one or more dummy vias110C (dummy holes 106C) are preferably connected to the branch pointbetween the wide interconnect portion and the narrow interconnectportion or to part of the wide interconnect portion near the branchpoint. Then, vacancies which are to enter the narrow interconnectportion from the wide interconnect portion and flow into the via 110Aare effectively captured in the dummy vias 110C. The dummy vias 110C arenot necessarily provided only at the branch point or its neighboringportions. For example, if a dummy via 110C is located in part of thenarrow interconnect portion relatively near the wide interconnectportion, most of vacancies which are to enter the via 110A are capturedin the dummy via 110C before reaching the via 110A. Accordingly, it ispossible to prevent occurrence of a void in the via 110A. As a result,the number of devices malfunctioning when held at high temperature isfurther reduced.

Embodiment 3 A Case where a Via and a Dummy Via are Provided in the SameLayer (with a Smaller Dummy Via)

Hereinafter, an interconnection structure and a method for forming thestructure according to a third embodiment of the present invention willbe described with reference to the drawings.

FIG. 8A is a cross-sectional view showing the interconnection structureof the third embodiment. FIG. 8B is a plan view showing the multilevelinterconnection structure shown in FIG. 8A when viewed from above. InFIGS. 8A and 8B, components already described in the first embodimentwith reference to FIGS. 1A through 1C and 2A through 2C are denoted bythe same reference numerals, and detailed description thereof will beomitted.

As shown in FIGS. 8A and 8B, the third embodiment is different from thefirst embodiment in the following ways. Instead of the dummy hole 106B,a dummy hole 106D with a diameter smaller than that of the dummy hole106B is provided and a dummy via 110D is provided in the dummy hole 106Dinstead of the dummy via 110B. That is, in this embodiment, the diameterof the dummy hole 106D (the dummy via 110D) is smaller that of a viahole 106A (a via 110A).

In this embodiment, the dummy via 110D is connected to a secondinterconnect 111 near the via 110A.

As shown in FIG. 8A, neither a dummy interconnect 102B nor the dummy via110D constitutes a closed circuit in actual use. In other words, even ifthe dummy via 110D is omitted in the interconnection structure shown inFIG. 8A, a device with this interconnection structure is operable atleast immediately after fabrication.

In addition, in this embodiment, the width of each of a firstinterconnect 102A and the dummy interconnect 102B is smaller than thatof the second interconnect 111, as shown in FIG. 8B. Specifically, thewidth of each of the first interconnect 102A and the dummy interconnect102B is, for example, 0.2 μm, the diameter of the via 110A (the via hole106A) is, for example, 0.20 μm, the diameter of the dummy via 110D (thedummy hole 106D) is, for example, 0.16 μm, and the width of the secondinterconnect 111 is, for example, 10 μm. The space between the via 110Aand the dummy via 110D, more specifically, the space between the edge ofthe via 110A toward the dummy via 110D and the edge of the dummy via110D toward the via 110A is 0.24 μm, for example.

A method for forming the multilevel interconnection structure shown inFIG. 8A according to the third embodiment is different from that of thefirst embodiment (shown in FIGS. 1A through 1C, 2A and 2B) only in thatthe dummy hole 106D reaching the dummy interconnect 102B and having adiameter smaller than that of the dummy hole 106B is formed instead ofthe dummy hole 106B in the process step shown in FIG. 1B. That is, thelayout of a mask pattern for forming the dummy hole only needs to bechanged.

With the foregoing interconnection structure and the method for formingthe structure according to the third embodiment, a highly-reliablemultilevel interconnection structure which hardly causes malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The dummy via 110D is provided on the secondinterconnect 111 near the via 110A, so that vacancies in a part of theconductive film (the Cu film 109) constituting the second interconnect111 are divided and respectively flow into the via 110A and the dummyvia 110D. That is, the dummy via 110D reduces the number of vacanciesflowing into each via so that the stress gradient from the secondinterconnect 111 to the via 110A is reduced. Accordingly, even when theinterconnection structure is held at high temperature, flowing ofvacancies from the second interconnect 111 into the via 110A issuppressed. As a result, plastic deformation of a part of the conductivefilm (the Cu film 109) constituting the via 110A, i.e., occurrence of avoid inside the via hole 106A, is suppressed, so that a highly-reliablemultilevel interconnection structure which hardly causes malfunctioneven when held at high temperature is implemented.

In the third embodiment, the resultant multilevel interconnectionstructure is more reliable than that obtained in the first embodiment.This is because of the following reasons. In this embodiment, thediameter of the dummy hole 106D (the dummy via 110D) is smaller thanthat of the via hole 106A (the via 110A). In other words, the volume ofthe dummy via 110D is smaller than that of the via 110A. Accordingly,the stress gradient between the second interconnect 111 and the dummyvia 110D is steeper than that between the second interconnect 111 andthe via 110A, so that flowing of vacancies from the part of theconductive film (the Cu film 109) constituting the second interconnect111 into the dummy via 110D precedes that into the via 110A. This moreeffectively suppresses plastic deformation of the part of the conductivefilm (the Cu film 109) constituting the via 110A, i.e., occurrence of avoid in the via hole 106A. As a result, the resultant multilevelinterconnection structure is more reliable than that obtained in thefirst embodiment.

In addition, in the third embodiment, the dummy interconnect 102B isprovided under the dummy via 110D (the dummy hole 106D). Accordingly,the dummy hole 106D is easily formed by etching the SiO₂ film 104 andthe SiN film 103 with the dummy interconnect 102B used as an etchingstopper.

In the third embodiment, the space between the via 110A and the dummyvia 110D (i.e., the space between the via hole 106A and the dummy hole106D: hereinafter referred to as a via-to-dummy via space) is preferablyas small as possible. To obtain the effect of reducing the number ofvacancies flowing into the via 110A by using the dummy via 110D, thevia-to-dummy via space is preferably 25 μm or less and is morepreferably 1 μm or less. Then, part of vacancies which are to flow intothe via 110A flow into the dummy via 110D. The minimum via-to-dummy viaspace can be set in accordance with the minimum isolation width (e.g.,0.2 μm) between interconnects or vias defined by the design rule, forexample. If the minimum isolation width between interconnects is setsubstantially equal to the minimum interconnect width, the minimumvia-to-dummy via space may be set in accordance with the minimuminterconnect width.

In the third embodiment, the number of dummy vias 110D provided for onevia 110A is preferably as large as possible. Specifically, it ispreferable to provide dummy vias 110D as many as possible on a part ofthe second interconnect 111 where the dummy vias 110D do not affectcircuit operation.

In addition, in the third embodiment, if the second interconnect 111includes a wide interconnect portion having a width of, for example,about 10 μm and a narrow interconnect portion having a width of, forexample, about 0.20 μm or less and branching off from the wideinterconnect portion and if the via 110A (the via hole 106A) isconnected to the narrow interconnect portion, one or more dummy vias110D (dummy holes 106D) are preferably connected to the branch pointbetween the wide interconnect portion and the narrow interconnectportion or to part of the wide interconnect portion near the branchpoint. Then, vacancies which are to enter the narrow interconnectportion from the wide interconnect portion and flow into the via 110Aare effectively captured in the dummy via 110D. The dummy vias 110D arenot necessarily provided only at the branch point or its neighboringportions. For example, if a dummy via 110D is located on the narrowinterconnect portion relatively near the wide interconnect portion, mostof vacancies which are to enter the via 110A are captured in the dummyvia 110D before reaching the via 110A. Accordingly, it is possible toprevent occurrence of a void in the via 110A. As a result, the number ofdevices malfunctioning when held at high temperature is further reduced.

Moreover, in the third embodiment, instead of the dummy interconnect102B, the dummy via 110D (the dummy hole 106D) may be formed such thatthe bottom of the dummy via 110D is located in the insulating film 101.Then, the dummy hole 106D is deeper than the via hole 106A. This makesthe stress gradient between the second interconnect 111 and the dummyvia 110D much steeper than that between the second interconnect 111 andthe via 110A as compared to the first embodiment. Accordingly, flowingof vacancies from the part of the conductive film (the Cu film 109)constituting the second interconnect 111 into the dummy via 110Dprecedes that into the via 110A. This more effectively suppressesplastic deformation of the part of the conductive film (the Cu film 109)constituting the via 110A, i.e., occurrence of a void in the via hole106A. As a result, the reliability of the resultant multilevelinterconnection structure is further enhanced.

Embodiment 4 A Case where a Via and a Dummy Via are Provided in the SameLayer (Where the Shape of a Dummy Via is Changed)

Hereinafter, an interconnection structure and a method for forming thestructure according to a fourth embodiment of the present invention willbe described with reference to the drawings.

FIG. 9A is a cross-sectional view showing the interconnection structureof the fourth embodiment. FIG. 9B is a plan view showing the multilevelinterconnection structure shown in FIG. 9A when viewed from above. InFIGS. 9A and 9B, components already described in the first embodimentwith reference to FIGS. 1A through 1C and 2A through 2C are denoted bythe same reference numerals, and detailed description thereof will beomitted.

As shown in FIGS. 9A and 9B, the fourth embodiment is different from thefirst embodiment in the following ways. Instead of the dummy hole 106B,a dummy trench 106E which has a shape different from that of the dummyhole 106B (i.e., the via hole 106A), more specifically, which is longerthan the via hole 106A in a plan view, is provided. In addition, insteadof the dummy via 110B, a dummy portion 110E is provided in the dummytrench 106E. The dummy trench 106E (the dummy portion 110E) isrectangular, for example, in the plan view. The length (i.e., the longersides) of the dummy portion 110E and the width (i.e., the shorter sides)of a second interconnect 111 are provided along the same direction inthe plan view. The dummy portion 110E is connected to the secondinterconnect 111 near a via 110A (the via hole 106A). The dummy portion110E is closer to the center of the second interconnect 111 than the via110A is. In other words, the distance between the via 110A and the endof the second interconnect 111 opposite the via 110A with respect to thedummy portion 110E is longer than the distance between the via 110A andthe other end of the second interconnect 111, i.e., the end of thesecond interconnect 111 toward the via 110A.

As shown in FIG. 9A, neither the dummy interconnect 102B nor the dummyportion 110E constitutes a closed circuit in actual use. In other words,even if the dummy portion 110E is omitted in the interconnectionstructure shown in FIG. 9A, a device with this interconnection structureis operable at least immediately after fabrication.

In addition, in this embodiment, the width of each of a firstinterconnect 102A and a dummy interconnect 102B is smaller than that ofthe second interconnect 111, as shown in FIG. 9B. Specifically, thewidth of each of the first interconnect 102A and the dummy interconnect102B is, for example, 0.2 μm, the diameter of the via 110A (the via hole106A) is, for example, 0.20 μm, the length and width of the rectangulardummy portion 110E (the dummy trench 106E) are, for example, 0.8 μm and0.20 μm, respectively, and the width of the second interconnect 111 is,for example, 10 μm. The space between the via 110A and the dummy portion110E, more specifically, the space between the edge of the via 110Atoward the dummy portion 110E and the edge of the dummy portion 110Etoward the via 110A is 0.2 μm, for example.

A method for forming the multilevel interconnection structure shown inFIG. 9A according to the fourth embodiment is different from that of thefirst embodiment (shown in FIGS. 1A through 1C, 2A and 2B) only in thatthe dummy trench 106E reaching the dummy interconnect 102B and having arectangular shape in a plan view is formed instead of the dummy hole106B in the process step shown in FIG. 1B. That is, the layout of a maskpattern for forming the dummy hole only needs to be changed.

With the foregoing interconnection structure and the method for formingthe structure according to the fourth embodiment, a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The dummy portion 110E is provided on the secondinterconnect 111 near the via 110A, so that vacancies in a part of aconductive film (a Cu film 109) constituting the second interconnect 111are divided and respectively flow into the via 110A and the dummyportion 110E. That is, the dummy portion 110E reduces the number ofvacancies flowing into each via so that the stress gradient from thesecond interconnect 111 to the via 110A is reduced. Accordingly, evenwhen the interconnection structure is held at high temperature, flowingof vacancies from the second interconnect 111 into the via 110A issuppressed. As a result, plastic deformation of a part of the conductivefilm (the Cu film 109) constituting the via 110A, i.e., occurrence of avoid inside the via hole 106A, is suppressed, so that a highly-reliablemultilevel interconnection structure which hardly causes malfunctioneven when held at high temperature is implemented.

In the fourth embodiment, the resultant multilevel interconnectionstructure is more reliable than that obtained in the first embodiment.This is because of the following reasons. In this embodiment, the dummytrench 106E (the dummy portion 110E) is longer than the via hole 106A(the via 110A) in a plan view and the length of the dummy portion 110Eand the width of the second interconnect 111 are provided along the samedirection in the plan view. Accordingly, vacancies which are present ina part of the conductive film (the Cu film 109) constituting the secondinterconnect 111 opposite the via 110A with respect to the dummy portion110E flow into the dummy portion 110E, so that it is possible to preventthese vacancies from reaching the via 110A. This more effectivelysuppresses plastic deformation of the part of the conductive film (theCu film 109) constituting the via 110A, i.e., occurrence of a void inthe via hole 106A. As a result, the resultant multilevel interconnectionstructure is more reliable than that obtained in the first embodiment.

In addition, in the fourth embodiment, the dummy portion 110E is closerto the center of the second interconnect 111 than the via 110A is. Inother words, the distance between the via 110A and the end of the secondinterconnect 111 opposite the via 110A with respect to the dummy portion110E is longer than the distance between the via 110A and the other endof the second interconnect 111, i.e., the end of the second interconnect111 toward the via 110A. Accordingly, the following advantage isobtained. A first region in the second interconnect 111 between the via110A and the end of the second interconnect 111 toward the dummy portion110E is larger than a second region in the second interconnect 111between the other end thereof and the via 110A, so that the first regioncontains a larger number of vacancies than the second region. The dummyportion 110E is provided on this first region in the second interconnect111, and thus vacancies more effectively flow into the dummy portion110E. This more effectively suppresses plastic deformation of the partof the conductive film (the Cu film 109) constituting the via 110A,i.e., occurrence of a void in the via hole 106A. As a result, thereliability of the resultant multilevel interconnection structure isfurther enhanced.

In addition, in the fourth embodiment, the dummy interconnect 102B isprovided under the dummy portion 110E (the dummy trench 106E).Accordingly, the dummy trench 106E is easily formed by etching the SiO₂film 104 and the SiN film 103 with the dummy interconnect 102B used asan etching stopper.

In the fourth embodiment, the space between the via 110A and the dummyportion 110E (i.e., the space between the via hole 106A and the dummytrench 106E: hereinafter referred to as a via-to-dummy via space) ispreferably as small as possible. To obtain the effect of reducing thenumber of vacancies flowing into the via 110A by using the dummy portion110E, the via-to-dummy via space is preferably 25 μM or less and is morepreferably 1 μm or less. Then, the effect of making part of vacancieswhich are to flow into the via 110A flow into the dummy portion 110E isensured. The minimum via-to-dummy via space can be set in accordancewith the minimum isolation width (e.g., 0.2 μM) between interconnects orvias defined by the design rule, for example. If the minimum isolationwidth between interconnects is set substantially equal to the minimuminterconnect width, the minimum via-to-dummy via space may be set inaccordance with the minimum interconnect width.

In the fourth embodiment, the number of dummy portions 110E provided forone via 110A is preferably as large as possible. Specifically, it ispreferable to provide dummy portions 110E as many as possible on a partof the second interconnect 111 where the dummy portions 110E do notaffect circuit operation.

In the fourth embodiment, the dummy interconnect 102B is not necessarilyprovided, and the dummy portion 110E (the dummy trench 106E) may beformed instead such that the bottom thereof is located in the insulatingfilm 101.

In the fourth embodiment, the planar shape of the via hole 106A (the via110A) different from that of the dummy trench 106E (the dummy portion110E) is not limited specifically, and may be a circle or a square, forexample.

Modified Example of Embodiment 4

Hereinafter, an interconnection structure and a method for forming thestructure according to a modified example of the fourth embodiment willbe described with reference to the drawings.

FIG. 10 is a plan view showing the interconnection structure accordingto the modified example of the fourth embodiment.

As shown in FIG. 10, this modified example is different from the fourthembodiment (see FIG. 9B) in the following ways. First, the secondinterconnect 111 includes: a wide interconnect portion 111 a having awidth of 10 μm, for example; and a narrow interconnect portion 111 bhaving a width of 0.20 μm, for example, and branching off from the wideinterconnect portion 111 a. Second, the via 110A (the via hole 106A) isconnected to the narrow interconnect portion 111 b. Third, the dummyportion 110E (the dummy trench 106E) is connected to the wideinterconnect portion 111 a near the branch point between the wideinterconnect portion 111 a and the narrow interconnect portion 111 b. Ina case where the narrow interconnect portion 111 b extends from a longerside of the wide interconnect portion 111 a as in this modified example,the length of the dummy portion 110E and the length of the wideinterconnect portion 111 a are provided along the same direction in theplan view, as shown in FIG. 10.

That is, the method for forming the interconnection structure accordingto this modified example is different from that of the fourth embodimentin that in the process step shown in FIG. 1B, the interconnect trench107 divided into a first trench with a relatively large width and asecond trench with a relatively small width is formed and the dummytrench 106E is also formed near the branch point between the firsttrench and the second trench.

In this modified example, not only the advantages obtained by the fourthembodiment but also the following advantage is obtained. Vacancies whichare to enter the narrow interconnect portion 111 b from the wideinterconnect portion 111 a and flow into the via 110A are effectivelycaptured in the dummy portion 110E. As a result, the number of devicesmalfunctioning when being held at high temperature is further reduced.

In addition, the advantage of this modified example obtained by usingthe dummy portion 110E (i.e., suppression of malfunction after a devicehas been held at high temperature) is remarkable especially when thewidth of the narrow interconnect portion 111 b is about 0.20 μm or less,as in the modified example of the first embodiment.

Embodiment 5 A Case where a Via and a Dummy Via are Provided inDifferent Layers

Hereinafter, an interconnection structure and a method for forming thestructure according to a fifth embodiment of the present invention willbe described with reference to the drawings.

FIG. 13B is a cross-sectional view showing the interconnection structureof the fifth embodiment. FIG. 13C is a plan view showing the multilevelinterconnection structure shown in FIG. 13B when viewed from above. InFIGS. 13B and 13C, components already described in the first embodimentwith reference to FIGS. 1A through 1C and 2A through 2C or the secondembodiment with reference to FIGS. 6A through 6C and 7A through 7C, forexample, are denoted by the same reference numerals, and detaileddescription thereof will be omitted.

As shown in FIGS. 13B and 13C, a first interconnect 102A is buried in aninsulating film 101 formed on a semiconductor substrate (not shown), anda SiN film 103, a SiO₂ film 104 and an FSG film 105 are formed in thisorder over the insulating film 101 and the first interconnect 102A. Avia hole 106A is formed through the SiO₂ film 104 and the SiN film 103to reach the first interconnect 102A. An interconnect trench 107 isformed through the FSG film 105 to reach the via hole 106A. A barrierfilm 108 and a Cu film 109 are buried in this order in the via hole 106Aand the interconnect trench 107, thereby forming a via 100A and a secondinterconnect 111 in the via hole 106A and the interconnect trench 107,respectively.

A SiN film 112, a SiO₂ film 113 and an FSG film 114 are formed over theFSG film 105 and the second interconnect 111. A dummy via hole (dummyhole) 115 is formed through the FSG film 114, the SiO₂ film 113 and theSiN film 112 to reach the second interconnect 111. A barrier film 116and a Cu film 117 are buried in this order in the dummy hole 115,thereby forming a dummy via 118 in the dummy hole 115. The dummy via 118is connected to the second interconnect 111 near the via 110A. A SiNfilm 119 is formed over the FSG film 114 and the dummy via 118.

As described above, this embodiment is greatly different from the firstthrough fourth embodiments in that the dummy hole 115 (the dummy via118) is not provided under the second interconnect 111 but is providedabove the second interconnect 111.

As shown in FIG. 13B, the dummy via 118 does not constitute any closedcircuit in actual use. In other words, even if the dummy via 118 isomitted in the interconnection structure shown in FIG. 13B, a devicewith this interconnection structure is operable at least immediatelyafter fabrication.

In addition, as shown in FIG. 13C, in this embodiment, the firstinterconnect 102A has a width smaller than that of the secondinterconnect 111. Specifically, the width of the first interconnect 102Ais, for example, 0.2 μm, the diameter of each of the via 110A (the viahole 106A) and the dummy via 118 (the dummy hole 115) is, for example,0.20 μm, and the width of the second interconnect 111 is, for example,10 μm. The space between the via 110A and the dummy via 118, morespecifically, the space between the edge of the via 110A toward thedummy via 118 and the edge of the dummy via 118 toward the via 110A is0.2 μm, for example.

FIGS. 11A through 11C, 12A through 12C and 13A are cross-sectional viewsshowing respective process steps of a method for forming the multilevelinterconnection structure shown in FIG. 13B according to the fifthembodiment.

First, as shown in FIG. 11A, an insulating film 101 is formed on thesurface of a semiconductor substrate (not shown), and then a firstinterconnect 102A is formed in the insulating film 101.

Next, as shown in FIG. 11B, a SiN film 103, a SiO₂ film 104 and a FSGfilm 105 are formed in this order over the insulating film 101 and thefirst interconnect 102A by a plasma CVD process, for example.Thereafter, lithography and dry etching are alternately performed twice(i.e., lithography and dry etching are each performed twice), therebyforming a via hole 106A in the SiO₂ film 104 and the SiN film 103 toreach the first interconnect 102A and also forming an interconnecttrench 107 in the FSG film 105 to reach the via hole 106A.

Then, as shown in FIG. 11C, a barrier film 108 is deposited by a PVDprocess, for example, to partly fill the via hole 106A and theinterconnect trench 107. Then, a Cu film 109 is formed by a platingprocess, for example, on the barrier film 108 to completely fill the viahole 106A and the interconnect trench 107.

Thereafter, as shown in FIG. 12A, parts of the barrier film 108 and theCu film 109 extending off the interconnect trench 107 are removed by aCMP process, for example. In this manner, a second interconnect 111 isformed in the interconnect trench 107. In addition, a via 110A is formedin the via hole 106A to connect the first interconnect 102A and thesecond interconnect 111 to each other.

Subsequently, as shown in FIG. 12B, a SiN film 112, a SiO₂ film 113 andan FSG film 114 are formed in this order by, for example, a plasma CVDprocess over the FSG film 105 and the second interconnect 111.Thereafter, lithography and dry etching are performed, and thereby adummy hole 115 is formed through the FSG film 114, the SiO₂ film 113 andthe SiN film 112 to reach the second interconnect 111.

Then, as shown in FIG. 12C, a barrier film 116 is formed by, forexample, a PVD process to partly fill the dummy hole 115. Thereafter, aCu film 117 is formed by, for example, a plating process on the barrierfilm 116 to completely fill the dummy hole 115.

Subsequently, as shown in FIG. 13A, parts of the barrier film 116 andthe Cu film 117 extending off the dummy hole 115 are removed by, forexample, a CMP process. In this manner, a dummy via 118 connected to thesecond interconnect 111 is formed in the dummy hole 115.

Lastly, a SiN film 119 is deposited over the FSG film 114 and the dummyvia 118 (the Cu film 117), thus completing the multilevelinterconnection structure shown in FIG. 13B.

With the foregoing interconnection structure and the method for formingthe structure according to the fifth embodiment, a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The dummy via 118 is provided on the secondinterconnect 111 near the via 110A, so that vacancies in a part of theconductive film (the Cu film 109) constituting the second interconnect111 are divided and respectively attracted to the via 110A and the dummyvia 118. Specifically, in a portion of the second interconnect 111connected to the dummy via 118, tensile stress on a part of the Cu film109 constituting the second interconnect 111 is lower than that on itssurrounding portions. Accordingly, vacancies inside the Cu film 109 areattracted to the dummy via 118, so that even when the interconnectionstructure is held at high temperature, flowing of vacancies from thesecond interconnect 111 into the via 110A is suppressed. As a result,plastic deformation of a part of the conductive film (the Cu film 109)constituting the via 110A, i.e., occurrence of a void inside the viahole 106A, is suppressed, so that a highly-reliable multilevelinterconnection structure which does not cause malfunction even whenheld at high temperature is implemented.

In the fifth embodiment, the space between the via 110A and the dummyvia 118 (i.e., the space between the via hole 106A and the dummy hole115: hereinafter referred to as a via-to-dummy via space) is preferablyas small as possible. To obtain the effect of reducing the number ofvacancies flowing into the via 110A by using the dummy via 118, thevia-to-dummy via space is preferably 25 μm or less and is morepreferably 1 μm or less. The minimum via-to-dummy via space can be setin accordance with the minimum isolation width (e.g., 0.2 μm) betweeninterconnects or vias defined by the design rule, for example. If theminimum isolation width between interconnects is set substantially equalto the minimum interconnect width, the minimum via-to-dummy via spacemay be set in accordance with the minimum interconnect width.

In the fifth embodiment, the number of dummy vias 118 provided for onevia 110A is preferably as large as possible. Specifically, it ispreferable to provide dummy vias 118 as many as possible on a part ofthe second interconnect 111 where the dummy vias 118 do not affectcircuit operation.

In the fifth embodiment, the top of the dummy via 118 is located in theinsulating films. Alternatively, the top of the dummy via 118 may beconnected to a dummy interconnect. In such a structure, after a hole forforming the dummy via 118 has been formed by etching, etching forforming a dummy interconnect trench is performed, thus ensuring removalof residues of the insulating film remaining on the bottom of the hole.Accordingly, connection of the dummy via 118 to the second interconnect111 is ensured, resulting in that advantages of this embodiment are alsoobtained in this case.

In the fifth embodiment, if the diameter of the dummy via 118 (the dummyhole 115) is smaller than that of the via 110A (the via hole 106A),advantages similar to those of the third embodiment are obtained.

In addition, in the fifth embodiment, if the dummy via 118 isrectangular in a plan view and the length of this dummy via 118 and thewidth of the second interconnect 111 are provided along the samedirection in the plan view, advantages similar to those of the fourthembodiment are obtained. In such a case, the dummy via 118 is preferablycloser to the center of the second interconnect 111 than the via 110Ais. In other words, if the distance between the via 110A and the end ofthe second interconnect 111 opposite the via 110A with respect to thedummy via 118 is longer than the distance between the via 110A and theother end of the second interconnect 111, i.e., the end of the secondinterconnect 111 toward the via 110A, the foregoing advantages becomemore remarkable. In such a case, the planar shape of the via hole 106A(the via 110A) is not specifically limited, and may be a circle or asquare, for example.

Embodiment 6 Insulating Slit 1

Hereinafter, an interconnection structure and a method for forming thestructure according to a sixth embodiment of the present invention willbe described with reference to the drawings.

FIG. 15B is a cross-sectional view showing the interconnection structureof the sixth embodiment. FIG. 15C is a plan view showing the multilevelinterconnection structure shown in FIG. 15B when viewed from above. InFIGS. 15B and 15C, components already described in the first embodimentwith reference to FIGS. 1A through 1C and 2A through 2C or the secondembodiment with reference to FIGS. 6A through 6C and 7A through 7C, forexample, are denoted by the same reference numerals, and detaileddescription thereof will be omitted.

As shown in FIGS. 15B and 15C, a first interconnect 102A is buried in aninsulating film 101 formed on a semiconductor substrate (not shown), anda SiN film 103, a SiO₂ film 104 and an FSG film 105 are formed in thisorder over the insulating film 101 and the first interconnect 102A. Avia hole 106A is formed through the SiO₂ film 104 and the SiN film 103to reach the first interconnect 102A. An interconnect trench 107 isformed through the FSG film 105 to reach the via hole 106A. A barrierfilm 108 and a Cu film 109 are buried in this order in the via hole 106Aand the interconnect trench 107, thereby forming a via 110A and a secondinterconnect 111 in the via hole 106A and the interconnect trench 107,respectively.

A characteristic of this embodiment is that a pair of insulating slits120 is provided in the second interconnect 111 to sandwich a portion ofthe second interconnect 111 connected to the via 110A (a portion of thesecond interconnect 111 on the via 110A.) In this embodiment, theinsulating slits 120 are made of part of the FSG film 105 as aninterlayer dielectric film. A SiN film 112 is formed over the FSG film105 including the insulating slits 120 and the second interconnect 111.

As shown in FIG. 15C, in this embodiment, the first interconnect 102Ahas a width smaller than that of the second interconnect 111.Specifically, the width of the first interconnect 102A is, for example,0.2 μm, the diameter of the via 110A (the via hole 106A) is, forexample, 0.20 μm, and the width of the second interconnect 111 is, forexample, 10 μm. The shape of each of the insulating slits 120 isrectangular in a plan view, and the length of each of the insulatingslits 120 is greater than or equal to twice and less than or equal tofour times as large as the diameter of the via 110A in the plan view.For example, the length and width of each of the insulating slits 120 inthe plan view is 0.4 μm and 0.2 μm, respectively. In this embodiment, alonger side of each of the insulating slits 120 is in contact with theportion of the second interconnect 111 connected to the via 110A.

FIGS. 14A through 14C and FIG. 15A are cross-sectional views showingrespective process steps of a method for forming the multilevelinterconnection structure shown in FIG. 15B according to the sixthembodiment.

First, as shown in FIG. 14A, an insulating film 101 is formed on thesurface of a semiconductor substrate (not shown), and then a firstinterconnect 102A is formed in the insulating film 101.

Next, as shown in FIG. 14B, a SiN film 103, a SiO₂ film 104 and a FSGfilm 105 are formed in this order over the insulating film 101 and thefirst interconnect 102A by a plasma CVD process, for example.Thereafter, lithography and dry etching are alternately performed twice(i.e., lithography and dry etching are each performed twice), therebyforming a via hole 106A in the SiO₂ film 104 and the SiN film 103 toreach the first interconnect 102A and also forming an interconnecttrench 107 in contact with the via hole 106A in the FSG film 105. Inthis embodiment, in forming the interconnect trench 107, part of the FSGfilm 105 is left in the interconnect trench 107 to surround the via hole106A, thereby forming insulating slits 120. Specifically, in alithography process for forming the interconnect trench 107, a resistpattern covering not only the part of the FSG film 105 except for aregion where the interconnect trench 107 is to be formed but also a partof the FSG film 105 to be the insulating slits 120 is used. Then, theFSG film 105 is etched using the resist pattern as a mask.

Then, as shown in FIG. 14C, a barrier film 108 is deposited by a PVDprocess, for example, to partly fill the via hole 106A and theinterconnect trench 107. Then, a Cu film 109 is formed by a platingprocess, for example, on the barrier film 108 to completely fill the viahole 106A and the interconnect trench 107.

Thereafter, as shown in FIG. 15A, parts of the barrier film 108 and theCu film 109 extending off the interconnect trench 107 are removed by aCMP process, for example. In this manner, a second interconnect 111 isformed in the interconnect trench 107. In addition, a via 110A is formedin the via hole 106A to connect the first interconnect 102A and thesecond interconnect 111 to each other.

Lastly, a SiN film 112 is deposited over the FSG film 105 including theinsulating slits 120 and the second interconnect 111 (the Cu film 109),thus completing the multilevel interconnection structure shown in FIG.15B.

With the foregoing interconnection structure and the method for formingthe structure according to the sixth embodiment, a highly-reliablemultilevel interconnection structure which hardly causes malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The insulating slits 120 are provided near aportion of the second interconnect 111 connected to the via 110A. Thisportion of the second interconnect 111 will be also referred to as avia-connected portion. Specifically, the insulating slits 120 areprovided in the second interconnect 111 to be in contact with thevia-connected portion of the second interconnect 111. Accordingly,tensile stress on a part of the second interconnect 111 near thevia-connected portion is lower than that on the other part of the secondinterconnect 111. The insulating slits 120 reduce the number ofvacancies flowing into each via, so that the stress gradient from thesecond interconnect 111 to the via 110A is reduced, so that even whenthe interconnection structure is held at high temperature, flowing ofvacancies from the second interconnect 111 into the via 110A issuppressed. In addition, the insulating slits 120 are made of a materialdifferent from that for the conductive film (the Cu film 109)constituting the second interconnect 111 and the via 110A, so that theinsulating slits 120 act as barriers against movement of atoms orvacancies in the conductive film. This prevents convection of atomsinside the second interconnect 111 and the via 110A or accumulation ofvacancies on the bottom of the via 110A. As a result, plasticdeformation of a part of the conductive film (the Cu film 109)constituting the via 110A, i.e., occurrence of a void inside the viahole 106A, is suppressed, so that a highly-reliable multilevelinterconnection structure which hardly causes malfunction even when heldat high temperature is implemented.

FIG. 16 is a graph for explaining effects of this embodiment. In FIG.16, the ordinate indicates “the number of devices malfunctioning afterbeing held at high temperature” and the abscissa indicates “the presenceof an insulating slit”. The case of “with slit” corresponds to thisembodiment and the case of “without slit” corresponds to a conventionalexample. As shown in FIG. 16, in the case of “with insulating slit” inthis embodiment, “the number of devices malfunctioning when being heldat high temperature” is reduced to about one-eighth of that in the caseof “without slit”. This is because a slit made of an insulating filmprevents a phenomenon in which atoms in a conductive film forinterconnection move and vacancies in the conductive film gather in avia. Specifically, if a slit made of an insulating material differentfrom a material for an interconnect is present in an conductive film forinterconnection, this slit acts as a barrier against movement of atomsin the conductive film and also suppresses formation of a void resultingfrom gathering of vacancies from the conductive film in a via.Accordingly, in the case of “with insulating slit” in this embodiment,the number of devices malfunctioning when being held at hightemperature” is reduced.

In addition, in the sixth embodiment, each of the insulating slits 120is rectangular in a plan view. The length of each of the insulatingslits 120 is greater than or equal to twice and less than or equal tofour times as large as the diameter of the via 110A in the plan view. Alonger side of each of the respective insulating slits 120 in the planview is in contact with a portion of the second interconnect 111connected to the via 110A. Accordingly, the foregoing advantages areensured.

In the sixth embodiment, the shape and the number of the insulatingslits 120 (the number of the insulating slits 120 provided for one via110A) are not specifically limited.

In the sixth embodiment, part of the FSG film 105 is used as theinsulating slits 120. Alternatively, other insulating materials may beused instead. The insulating slits 120 may be replaced with slits madeof another conductive material different from a conductive materialconstituting the second interconnect 111 and the via 110A.

Further, in the sixth embodiment, the insulating slits 120 are notnecessarily in contact with the portion of the second interconnect 111connected to the via 110A. However, in a case where the insulating slits120 and the via-connected portion of the second interconnect 111 areapart from each other, the space between each of the insulating slits120 and the via-connected portion of the second interconnect 111, i.e.,the space between each of the insulating slits 120 and the via 110A, ispreferably 1 μm or less in order to ensure the foregoing advantages.

Furthermore, in the sixth embodiment, in a case where the secondinterconnect 111 includes: a wide interconnect portion having a width ofabout 10 μm, for example; and a narrow interconnect portion having awidth of about 0.20 μM or less, for example, and branching off from thewide interconnect portion and if the via 110A (the via hole 106A) isconnected to the narrow interconnect portion, one or more insulatingslits 120 are preferably connected to the branch point between the wideinterconnect portion and the narrow interconnect portion or a part ofthe wide interconnect portion near the branch point. Then, vacancieswhich are to enter the narrow interconnect portion from the wideinterconnect portion and flow into the via 110A are effectively capturedin the insulating slits 120. As a result, the number of devicesmalfunctioning when being held at high temperature is further reduced.

Embodiment 7 Insulating Slit 2

Hereinafter, an interconnection structure and a method for forming thestructure according to a seventh embodiment of the present inventionwill be described with reference to the drawings.

FIG. 17A is a cross-sectional view showing the interconnection structureof the seventh embodiment. FIG. 17B is a plan view showing themultilevel interconnection structure shown in FIG. 17A when viewed fromabove. In FIGS. 17A and 17B, components already described in the firstembodiment with reference to FIGS. 1A through 1C and 2A through 2C orthe sixth embodiment with reference to FIGS. 14A through 14C and 15Athrough 15C, for example, are denoted by the same reference numerals,and detailed description thereof will be omitted.

As shown in FIGS. 17A and 17B, the seventh embodiment is different fromthe sixth embodiment in the following ways. Instead of the insulatingslits 120 in contact with a portion of the second interconnect 111connected to the via 110A, an insulating slit 121 longer than theinsulating slits 120 is provided in the second interconnect 111 near thevia-connected portion of the second interconnect 111. In other words,the insulating slit 121 of this embodiment is not in contact with thevia-connected portion of the second interconnect 111. Specifically, theinsulating slit 121 is rectangular, for example, in a plan view and thelength of the insulating slit 121 and the width of the secondinterconnect 111 are provided along the same direction in the plan view.The insulating slit 121 is provided in the second interconnect 111 neara portion of the second interconnect 111 connected to the via 110A (thevia hole 106A) and is closer to the center of the second interconnect111 than the via 110A is. In other words, the distance between the via110A and the end of the second interconnect 111 opposite the via 110Awith respect to the insulating slit 121 is longer than the distancebetween the via 110A and the other end of the second interconnect 111,i.e., the end of the second interconnect 111 toward the via 110A.

As shown in FIG. 17B, in this embodiment, the first interconnect 102Ahas a width smaller than that of the second interconnect 111.Specifically, the width of the first interconnect 102A is, for example,0.2 μm, the diameter of the via 110A (the via hole 106A) is, forexample, 0.20 μm, and the width of the second interconnect 111 is, forexample, 10 μm. The length of the insulating slit 121 is greater than orequal to twice and less than or equal to ten times as large as thediameter of the via 110A in a plan view. For example, the length andwidth of the insulating slit 121 in the plan view is 0.8 μm and 0.2 μm,respectively. The space between the via 110A and the insulating slit121, more specifically, the space between the edge of the via 110Atoward the insulating slit 121 and the edge of the insulating slit 121toward the via 110A is 0.2 μm, for example.

A method for forming the multilevel interconnection structure shown inFIG. 17A according to the seventh embodiment is different from that ofthe sixth embodiment (see FIGS. 14A through 14C, 15A and 15B) in thefollowing ways. In the process step shown in FIG. 14B, morespecifically, in forming the interconnect trench 107, part of the FSGfilm 105 is left in the interconnect trench 107 to be slightly apartfrom the via hole 106A, thereby forming the insulating slit 121 longerthan the insulating slit 120, instead of the insulating slit 120.Specifically, in a lithography process for forming the interconnecttrench 107, the layout of a mask pattern for forming the insulating siltonly needs to be changed.

With the foregoing interconnection structure and the method for formingthe structure according to the seventh embodiment, a highly-reliablemultilevel interconnection structure which does not cause malfunctioneven when held at high temperature is implemented. This is because ofthe following reasons. The insulating slit 121 is provided near aportion of the second interconnect 111 connected to the via 110A, sothat tensile stress on a portion near the via-connected portion of thesecond interconnect 111 is lower than that on the other part of thesecond interconnect 111. The insulating slit 121 reduces the number ofvacancies flowing into each via, so that the stress gradient from thesecond interconnect 111 to the via 110A is reduced. Accordingly, evenwhen the interconnection structure is held at high temperature, flowingof vacancies from the second interconnect 111 into the via 110A issuppressed. In addition, the insulating slit 121 is made of a materialdifferent from that for the conductive film (the Cu film 109)constituting the second interconnect 111 and the via 110A, so that theinsulating slit 121 acts as a barrier against movement of atoms orvacancies in the conductive film. This prevents convection of atomsinside the second interconnect 111 and the via 110A or accumulation ofvacancies on the bottom of the via 110A. As a result, plasticdeformation of a part of the conductive film (the Cu film 109)constituting the via 110A, i.e., occurrence of a void inside the viahole 106A, is suppressed, so that a highly-reliable multilevelinterconnection structure which hardly causes malfunction even when heldat high temperature is implemented.

In the seventh embodiment, the reliability of the multilevelinterconnection structure is further enhanced because of the followingreasons. In this embodiment, the insulating slit 121 is rectangular in aplan view and the length of the insulating slit 121 and the width of thesecond interconnect 111 are provided along the same direction in theplan view. The insulating slit 121 is located near the portion of thesecond interconnect 111 connected to the via 110A. Accordingly, flowingof vacancies which are present in a part of the conductive film (the Cufilm 109) constituting the second interconnect 111 opposite the via 110Awith respect to the insulating slit 121 is blocked by the insulatingslit 121, so that these vacancies do not reach the via 110A. Inaddition, in this embodiment, the insulating slit 121 is closer to thecenter of the second interconnect 111 than the via 110A is. In otherwords, a first region in the second interconnect 111 between the via110A and the end of the second interconnect 111 opposite the via 110Awith respect to the insulating slit 121 is larger than a second regionin the second interconnect 111 between the via 110A and the other end ofthe second interconnect 111, i.e., the end of the second interconnect111 toward the via 110A. Therefore, the first region contains a largernumber of vacancies than the second region. In addition, the insulatingslit 121 is provided in this first region, so that movement of vacanciesis more effectively prevented. This more effectively suppresses plasticdeformation of the part of the conductive film (the Cu film 109)constituting the via 110A, i.e., occurrence of a void in the via hole106A. As a result, the reliability of the resultant multilevelinterconnection structure is further enhanced.

In the seventh embodiment, the space between the via 110A (the via hole106A) and the insulating slit 121 is preferably as small as possible. Toobtain the effect of reducing the number of vacancies flowing into thevia 110A by using the insulating slit 121, this space is preferably 1 μmor less. The insulating slit 121 may be in contact with a portion of thesecond interconnect 111 connected to the via 110A.

In the seventh embodiment, the shape and the number of the insulatingslit 121 (the number of insulating slits 121 provided for one via 110A)are not specifically limited.

In the seventh embodiment, part of the FSG film 105 is used as theinsulating slit 121. Alternatively, other insulating materials may beused. The insulating slit 121 may be replaced with a slit made ofanother conductive material different from a conductive materialconstituting the second interconnect 111 and the via 110A.

Moreover, in the seventh embodiment, if the second interconnect 111includes a wide interconnect portion having a width of, for example,about 10 μm and a narrow interconnect portion having a width of, forexample, about 0.20 μm or less and branching off from the wideinterconnect portion and if the via 110A (the via hole 106A) isconnected to the narrow interconnect portion, the insulating slit 121 ispreferably connected to the wide interconnect portion near the branchpoint between the wide interconnect portion and the narrow interconnectportion. In such a case, if the narrow interconnect portion extends froma longer side of the wide interconnect portion, the length of theinsulating slit 121 and the length of the wide interconnect portion areprovided along the same direction in the plan view. Then, vacancieswhich are to enter the narrow interconnect portion from the wideinterconnect portion and flow into the via 110A are effectively capturedin the insulating slit 121. As a result, the number of devicesmalfunctioning when held at high temperature is further reduced.

In the first through seventh embodiments, a SiO₂ film (e.g., the SiO₂film 104) and an FSG film (e.g., the FSG film 105) are used asinterlayer dielectric films between interconnects. However, the types ofthe interlayer dielectric films are not specifically limited.

In the first through seventh embodiments, a Cu film (e.g., the Cu film109) is used as an interconnect material. However, the type of theinterconnect material is not specifically limited. A material for abarrier film (e.g., the barrier film 108) is not specifically limited,either.

In the first through seventh embodiments, a SiN film (e.g., the SiN film112) is formed as a protective film over a damascene interconnect (e.g.,the first interconnect 102A or the second interconnect 111). However,this SiN film may not be formed.

The dummy vias and the insulating slits of the first through seventhembodiments may be, of course, combined in various manners in order toachieve a technical idea of the present invention, “movement ofvacancies in a conductive film for an interconnect is suppressed so thatoccurrence of a void in the interconnect after formation thereof isprevented.”

1. A method for fabricating a semiconductor device comprising the stepsof: (a) forming a first interconnect on a semiconductor substrate; (b)forming a first insulating film on the first interconnect; (c) formingin the first insulating film, a via hole connected to the firstinterconnect, a dummy hole which is arranged so as to be incapable ofhaving current flow therethrough, and an interconnect trench connectedto the via hole and the dummy hole; and (d) depositing a conductivematerial in the via hole, the dummy hole and the interconnect trench,thereby forming a via, a dummy via and a second interconnect.
 2. Themethod of claim 1, wherein in the step (a) a first dummy interconnect issimultaneously formed on the semiconductor substrate, and in the step(c) the dummy hole is connected to the first dummy interconnect.
 3. Themethod of claim 1, wherein in the step (c) the interconnect trench iscomprised of a first interconnect trench portion and a secondinterconnect trench portion whose width is smaller than that of thefirst interconnect trench portion and which branches from the firstinterconnect trench portion, and the via hole and the dummy hole areconnected to the interconnect trench.
 4. The method of claim 3, whereinin the step (c) the dummy hole is connected to the branch point betweenthe first and second interconnect trench portions or to the interconnecttrench near the branch point.
 5. The method of claim 1, wherein thefirst insulating film has a multilayer structure including a SiN filmand a SiO₂ film.
 6. The method of claim 1, wherein each of the first andsecond interconnects is connected to another element or an externalelectrode.
 7. The method of claim 1, wherein the first interconnect hasa width smaller than that of the second interconnect.
 8. The method ofclaim 2, wherein the first dummy interconnect has a width smaller thanthat of the second interconnect.
 9. The method of claim 1, wherein thevia and the dummy via are substantially circular in a plan view.
 10. Themethod of claim 1, wherein a planar shape of each of the via and thedummy via is substantially a square.
 11. The method of claim 1, whereinthe first interconnect and the second interconnect extend in a samedirection.
 12. The method of claim 1, wherein the dummy via is providedon an extended line along which the first interconnect extends.
 13. Themethod of claim 1, wherein the via and the dummy via are spaced at adistance of 25 μm or less.
 14. The method of claim 1, wherein a bottomof the dummy via is located deeper than a bottom of the via.
 15. Themethod of claim 1, wherein the second interconnect is comprised of afirst interconnect portion and a second interconnect portion whoseinterconnect width is smaller than that of the first interconnectportion and which branches from the first interconnect portion, and thevia is connected to the second interconnect portion.
 16. The method ofclaim 15, wherein the dummy via is formed at or near the branch pointbetween the first and second interconnect portions.
 17. The method ofclaim 15, wherein the dummy via is substantially rectangular in a planview, and a longer side of the dummy via and a longer side of the firstinterconnect portion are provided along a same direction.
 18. The methodof claim 1, wherein the dummy via and the second interconnect are madeof the same conductive film.
 19. The method of claim 1, wherein thedummy via includes a first and second end, the first end connected tothe second interconnect and the second end surrounded by a secondinsulating film.
 20. The method of claim 1, wherein the dummy viaincludes a first and second end, the first end connected to the secondinterconnect and the second end connected to a first dummy interconnect,the first dummy interconnect being surrounded by a second insulatingfilm.